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    <title>两数相加会产生新数</title>
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    <h1>JavaScript 数字</h1>
    <p>如果您对两个数相加，结果将是一个数：</p>
    <p id="demo"></p>
    <script>
        var x = 10;
        var y = 20;
        var z = x + y;
        document.getElementById("demo").innerHTML = z;
    </script>
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